Solar energy harvesting mystery solved by Irish and Qatari scientists

11 May 2015

Scientists in Dublin and Qatar have made a breakthrough in understanding how materials like crystals used to capture solar energy actually work, enabling them to improve the technology.

The breakthrough was made by Professor Stefano Sanvito, acting director at AMBER, the Science Foundation Ireland funded materials science centre based at Trinity College Dublin, and his team, in collaboration with researchers at the Qatar Environment and Energy Research Institute.

This discovery will now allow researchers to design even more efficient solar harvesting materials, using the knowledge gained from being able to map these materials. This research has this week been published in the prestigious scientific journal Nature Communications.

Hybrid organic/inorganic perovskites, which have been used as highly-efficient solar harvesting materials, are compounds where an inorganic crystal (like a standard semiconductor or metal) is interposed with organic molecules, also arranged in a crystal-like structure.

While it has been known in recent years that solar energy harvesting is extremely efficient in these materials, scientists did not understand how they worked.

Now AMBER researchers have the answer: by using state-of-the-art material modelling simulation tools (a process that involves creating and analysing a digital prototype of a physical model or material to predict its performance in the real world) and focusing specifically on the electronic properties of these materials, the researchers have revealed that the light is “captured” by the inorganic crystal alone.

What makes this material different to other solar harvesting materials, however, is that the electronic structure of these inorganic crystals is changed because of the motion of the molecules.

Solar breakthrough has implications for our planet

“Every hour the Sun irradiates the Earth with as much energy as that used by the entire planet in one year. Harvesting such enormous energy in an efficient and cost-effective way would mean abundant green energy for the entire human race,” Professor Sanvito said.

“Developing and improving our knowledge of solar energy harvesting is crucial. This is an exciting discovery. Now that we understand how these new materials work we can design new compounds to use for solar energy harvesting. A further advantage is that the materials can be grown chemically and not with expensive high-temperature processes.”

Silicon is the most commonly-used material in solar harvesting. There are ample amounts of silicon on our planet, and it is also a non-toxic material. However, its manufacturing process is expensive. This means that a standard solar panel will have a payback time (the time needed to pay back the energy used in creating it) of several years.

The perovskite materials have only recently entered the solar energy harvesting arena and have made progress at unprecedented speed. In only two years solar cells made of such materials have improved the efficiency from 1pc to more than 20pc. A further advantage is that these materials can be grown chemically and do not use expensive high-temperature processes, unlike silicon.

A solar cell made of these perovskites has a payback time of three months.

Unfortunately, although very efficient, to date these new materials have been shown to be unstable in humidity and contain lead, a toxic element. However, due to this new research, new compounds can be designed to eliminate these drawbacks.

“This discovery opens up a new avenue for the design of solar harvesting materials, which could result in increased energy efficiency as well as reduced costs,” said Dr Mohammad Khaleel, QEERI’s executive director.

“We are looking forward to continuing collaboration with AMBER to develop this further.”

Solar harvesting image via Shutterstock


John Kennedy is a journalist who served as editor of Silicon Republic for 17 years